Lubricating oils are widely used to reduce friction, protect against corrosion, and anticipate heat build-up in a variety of applications. Because such properties are seldom all achieved to a satisfactory degree using a lubricating oil alone, various additives have been developed for lubricating oil base stocks to improve their performance, e.g., anti-oxidants, viscosity index (VI) modifiers, flow improvers, corrosion inhibitors, etc.
Lubricating oils are a selected fraction of refined mineral oils used for the lubrication of (usually metallic) moving surfaces ranging from small precision machinery to the heaviest equipment. The oils generally contain small amounts of additives to impart desired properties such as viscosity and detergency, and range in viscosity from thin liquids to grease-like substances; unlike lubricating greases, they contain no solid or fibrous materials.
As used herein the term "lubricating oil" extends to a wide variety of oils having lubricative abilities including: automotive oils, heavy duty oils, marine oils, railroad oils, aviation lube oils, transmission fluids, hydraulic fluids, etc.
Lubricating oils are complex mixtures and, particularly when used in an internal combustion engine, are susceptible to breakdown caused by the high temperatures encountered during operation. While the chemistry of such breakdown is not fully understood, it is believed that oxidation plays a significant role, and for this reason it is known to add anti-oxidants to lubricating oils intended for such use.
The instant invention is directed to a technique which minimizes or entirely obviates the necessity of incorporating additives into baseoils for purposes of reducing engine build-up by virtue of the pretreatment which is performed. In effect, the pretreatment involves the removal of coking precursors from the baseoils. Although not performed for the same purpose, nor with the same objective, procedures do exist in which oils are treated for purposes of removing deposits and other undesired substances from oils.
Thus, removal is performed in certain processes which determine the amount of deposit removed as a measure of the tendency of the oil to coke.
U.S. Pat. No. 3,248,327 discloses one such technique which is a test known as a the Coker Detergency Test. This test is a modification of the Pratt and Whitney Test as described in United Stated Air Force Military Specification MIL-L-7808A. The test involves splashing the test oil in an air atmosphere against a heated aluminum panel for a given period of time and thereafter determining the amount of deposit formed on the panel. The oil is splashed onto the underside of an aluminum panel, and after a set period of time the test is stopped, and the aluminum panel is washed to remove excess non-coked oil. It is assumed that any increase in the weight of the panel, after washing and drying, must be due to coke formation on the aluminum. Similar techniques are disclosed in U.S. Pat. Nos. 3,095,377 and 3,153,622, and are identified as Panel Coker Tests meeting United States Air Force Specification MIL-L-9236A.
In yet another such testing technique deposits are removed, see U.S. Pat. Nos. 2,812,319 and 2,716,089. In these patents oil is heated in an aluminum measuring cup for a set period of time, after which the heated oil is permitted to settle without stirring. Thereafter the cycle is repeated a number of times, after which the oil is poured out of the cup, and the cup weighed to determine any increase in weight which would be indicative of coking.
The above techniques are clearly intended to be used only as small scale sampling techniques which permit one to determine the tendency of an oil to form coke deposits, by weighing the deposits formed in a sample.
Besides being treated for purposes of removing indicative amounts of coke deposits, oils have previously been treated also for the removal of asphaltene as part of well known techniques in the petroleum industry for removing metals which adhere to the asphaltene in petroleum residues. However, other than for purposes of removing metals, asphaltenes themselves were not previously removed on a regular basis as a technique for reducing the coking tendency of baseoils. Thus, where metals removal is either not a concern, or is performed by other techniques, there would previously have been no reason for removing the asphaltenes.